Carrier telegraph circuits



Jan. 1925- 1,521,674

L. ESPENSCHIED CARRIER TELEGRAPH CIRCUIT$ Filed 21, 1920 T g "4? Fr nu nn 16E INVEN'iOR ATTORNEY Patented Jan. 5, 1925.

LLO P QHIEQ Q QUEENS, N YORK;

ASSIGHGRJTO e l'IEfv' eN ELE H E nun rn nenann COMPANY, A conroaarron or new Yo'nig.

CARRIER rrnnnennrn crncnrrs;

Application filed October 21, 1922). Serial No.- 218;482'.

One of the objects of the invention has reference to the provision of arrangement whereby signals may be repeated from a carrier circuit to a low frequency telegraph circuit without the use of mechanical repeating relays.

Another object of the invention has ref erence to the provision of an arrangement of the character just described in which a local subscribers circuit or loop may be associated with the repeating apparatus to receive signals repeated from the carrier circuit to the low frequency telegraph line or vice versa, and to transmit signals to either ofsaid circuits through the repeater.

Another object of the invention is to provide a detector arrangement for association with a receiving carrier channel, said detector arrangement being so organized that carrier frequencies may be translated into the signaling currents of opposite sign.

Qther and further objects of the invention will be clear from the following description when read in connect-ion with the accompanying drawing, Fig. l of which constitutes a circuit diagram embodying a form of invention adapted for half duplex operation and Fig. 2 of which is a circuit diagram of a form of the invention adapted for full duplex operation.

Referring to Fig. 1, ML? designates a. transmission line 'over which carrier currents may be transmitted, said line bein associated through the transformer witi the common transmitting circuit TLW and the connnon receiving circuit RLWV, an artificial line or net-work hlNlV being pro- {itlQCl to balance the main line. In practice a plurality of carrier transmitting and receiving channels will be associated with each of the circuits TLlV and RLlV. For purpose of illustration, however, but a single transmitting channel is shown associated with the circuit .lLW and but a single recelving channel is shown associated with the circuit RLVV. The transmitting channel includes a transmitting amplifier TA which may be of any known construction as, for example, a vacuum tube amplifier. A source of carrier frequency G isillustrated as being connected with the input circuit of the" amplifier through a suitable filter F. The source G may be of any suitable arrangement for producing alternating current of any desired frequency but is preferablya vacuum tube oscillator. The receiving channel in-v cludes a receiving amplifier RA; similar to the amplifier TA and the detector D which may be of any known construction as, for example, a vacuum tube detector;

A metallic telegraph circuit is indicated at MLE, said metallic telegraph circuit being balanced by an artificial line of network MNE. A receiving polar relay RE of the balanced bridge type is associated with the line MLE; A transmittii'ig cl'iannel TLE is connected at the junction point of the'line MLE and the balancing circuit MNE. A receiving channel RLE for'the' mainline MLE' is connect-ed to the midpoints of the bridge circuit 11 Thepolarreceiving relay RE comprises windings included in them-am line MLE and the balancing circuit MNE on either side of the junction point of said circuit with thetransmittingcireuit TILE and said relay also includes windings in the bridge circuit 11 on either side of its junction with the receiving circuit RLE.

The balanced bridge arrangement, above described, i'ssuch that thecircuits TLE and RLE will be substantially conj u'gatel The receiving channel RLE is directlyconnected-to the carriertransnlittingchannel illustrated in such a manner that the telegraph currents of opposite sign received from the meta llic'lineh/ILE will modulate-the carrier frequency transmittedfrom the generator G to themain carrier line Milli. For this purpose t'he'channel RLE is connected to the terminals of the potentiometer in the in- Put circuit of the amplifier TA and theterininals of the oscillator- G are connected to the same points. The modulating amplifier TA. has such a potential normally impressed upon its grid by means of a grid battery that the metallic Morse currei'it of marking polarity received from the metallic line MLE, when superposed upon the normal grid potential will cause the tube to operate on a point of its characteristic curve corresponding to maximum amplification while the spacing polarity when superposed upon the normal grid potential shifts upon the point of operation to the lower knee of the curve. In this manner metallic Morse currents of opposite signs modulates the carrier frequency supplied by the generator G to produce considerable changes in the amplitude of the carrier currents transmitted over the main line MLlN.

, The transmitting channel TLE is directly connected to the circuits of the detector D independently of any mechanical relay arrangement for repeating the signals and hence the circuits of said detector must be arranged to translate the received modulated carrier currents into Morse currents of opposite signs. In order to accomplish this result the two conductors of TLE are connected through resistances 13 and 14 to opposite points of a Wheatstone bridge of which the plate filament impedance of the detector D forms one arm, a resistance 15 forms a second arm and the coils 16 and 17 of a transformer form the remaining arms. The plate battery of the detector D is connected across alternate points of the bridge circuit from the points to which the circuit TLE is connected. As is Well known the impedance of the detecting tube D will change with the amplitude of the carrier frequency impressed upon it and its input circuit is so adjusted that when a carrier frequency of maximum amplitude is impressed upon the tube, its output impedance will be less than that of the resistance arm 15 so that current will flow from the bridge points to the circuit TLE in one direction; when a carrier frequency of minimum amplitude is impressed upon the tube, its output impedance becomes greater than that of the resistance arm 15 and a current of the opposite sign flows to the circuit TLE. A secondary winding 18 is associated with the coils 16 and 17 of the bridge and is in effect associated with the bridge as regards the alternating current components of the detecting current in the same manner as the circuit TLE. By a proper adjustment of the transformer and the resistances 13 and 14 a desired ratio between the direct current component and he alternating current component of the detected signals supplied to the circuit TLE may be obtained.

In practice, it is desirable that means he provided whereby signals transmitted through the repeater arrangement may be received in a local circuit and signals may be sent form the local circuit through the repeater to the carrier line and the metallic line. For this purpose a loop L is provided,

said loop being balanced at one end by means of a balancing circuit N. Polar transmitting relays PE, PVV and PVV' are associated with the loop in such a manner that one winding will be included in the loop circuit and another in the balancing circuit. A polar receiving relay RVV is bridged across the circuit TLE and responds to the detected currents of opposite sign to transmit signals to the loop. The polar receiving relay RE associated with the metallic line ll lLE is also arranged to repeat signals to the loop through its armature. For this purpose, the junction point 19 between the loop L and the balancing circuit N is connected over a normal contact of the polar relay PW and normal contact of the receiving relay RlV and normal contact of the receiving relay RE to one pole of the divided battery B, and the opposite end of the loop is connected to the opposite pole of the battery. By means of this connection a greater current flows through the loop than flows through the balancing circuit and the loop windings of the polar relays PE, PH] and PW become effective to hold the armatures of said relays against their normal contacts. The alternate contact of the relays-EW' and El are connected to the opposite pole of the battery B from that connected to their normal contacts so that if the armature of either relay is shifted the battery connections at the opposite ends of the loop will be opposed and no current will flow in the loop. The alternate contact of the polar relay PW is connected directly with the same pole of the battery as that normally connected with the point 19 so that when the arn'iature of said relay is shifted the loop circuit is maintained in its normal condition and is unaffected by the operation of the receiving relay RE or RVV.

he polar transmitting relays PE and PW associated with the loop are so arranged that in response to the opening and closing of the loop the connections of the conductors of the circuits TLE and RLE may be reversed, thereby changing the polarity of the current which normally flows from the detector l) over the circuit Tlilt to the metallic line MLE and also changing the polarity of the current which normally flows from the metallic line MLE over the receiving circuit RLE to the modulating amplifier TA. if desired, a filter F may be included in the circuit R-LE to curb or round off the pulses of opposite sign transmitted to the modulating arrangement, thereby eliminatin some of the higher harmonics of the low frequencies in order to narrow the transmitted modulated band of frequencies.

The operation is as follows: the signals from a distant station associated with the metallic line MLE are transmitted by changing the polarity of the current flowing over said line. Each time the polarity is changed the polar relay responds and shifts its armature from negative to positive battery. As a consequence positive battery is connected to both ends of theloopgL and the Sounders not shown) in the loop are deenergized by reason that no current flows in the loop. The upper windings of the relays PE, PW and PW are deenergized but the current flowing in the lower windings is in the opposite direction from that normally flowing and consequently the armatures of said relays are held against their normal contacts.

The change in the polarity of the current incoming from the line MLE produces a similar change in the receiving circuit RLE. Assuming that the normal current transmitted over the line MLE is of marking polarity and that a current of spacing polarity is transmitted, the change in the grid potential of the amplifier TA is such that the tube works near the knee of its characteristic curve instead of at its point of maximum amplification. The amplitude of the oscillations transmitted from the generator G to the amplifier TA through the carrier line MLWV is, therefore, greatly decreased when a current of s acing polarity is received by the circuit LE. in this manner signals ma be transmitted from the metallic line M IE to the carrier circuit MLW, and it will be noted that no mechanical repeating is necessary, the action being purely one of modulation.

Signals may be transmittedfrom a distant station associated with the carrier circuit MLW by changing the amplitude ofthe carrier frequently transmitted. Assuming that when a current ofmaximum amplitude istransmitted a marking signal is being sent and when a carrier current of minimum amplitudeis transmitted a spacing signal is being sent, the received carrier frequency will he amplified by the amplifier RA and impressed upon the detector D. The grid circuit of the detector D may be soarranged that when a carrier current of maximum amplitude corresponding to a marking signal is impressed thereon the output impedance of the detector is smaller than that of the resistance 15 so that a current flows from the bridge points of the \Vheatstone bridge arrangement through the resistances 13 and 1% in one direction, and when carrier oscillations of minimumamplitude are impressed upon the grid circuit the impedance of the output of the detector D is greater than that of the resistance 15 and the current flows through resistances 13, and 14c in the opposite direction. The effect of the transformer arrangement comprising the coils 16, 17 and 18 is to accent the change in polarity at the beginningof each pulse by sup-erposing. the alternating; components upon the direct current change HDPFGSSBClthrough the resistances 13 and. 14: upon the;

circuit TE and the receiving: relay RVV,

lVhen the normal or marking current flowing from the resistances 13 and. I4 is changed to a current of spacin polarity the armature of the polar relay RTV is shifted and positive battery is connected to the point 19 so that the batte connections at the two ends of the loop are mutually opposed. Current, therefore, ceases to flow through the loop and the soundersin the loop respond. The current through the lower windings of the polar relays-PE, PW and PW is now inthe opposite direction so that, notwithstanding the decncrgization of the upper windings, the armatures remain against their normal contacts. in polarity of the current fiowing over'th'e resistances 13 and ll to the circuit TLE is impressed upon the midpoints of the low-er set of windings of the polar receiving relay RE so that the change in polarity is'transmitted to the metallic line MLE to actuate receiving apparatus assooiatedtheres with at a distant station. The polar relay R ho ever, is balanced with respect to the current thus transmitted and is unafiected thereby.

Since normally a current of one polarity, say the marking polarity, is transmitted fromthe metallic line MLE over the circuit R LE and atthe same time When signals are not being. transmitted in thev opposite direction a current of like polarity will be trans.- mitted from the detector D over thecircuit lLll to the metallic line MLE, it is possible to transmit signals in both: directions by merely changing the connections of the circuits RLE and thereby changing the polarity of the current normally flowing with respect to the modulating amplifier TA and with respectto the metallic line MLE, Whe t e lo p L is int a'up d in transmitting signals the current flowing ugh t e upp i ingof th p lar relays PE, PVV' and PYV ceases and the current flowing through the lower windings being} in normal direction said windings become effective to shift the armatures of the polar relays. The armatures of the polar relay PE change the connections of the circuit TLE thereby reversing the polarity of the current normally supplied bythe detector D to the metallic line So that a signal is transmitted to the latter. The polar relay PW reverses the connections of the circuit RLE thereby reversing the polarity of the current normally transmitted from the metallic line to the modulator T i. Modulated carriersignals will consequently be transmitted to the circuit lvlL'W. The polar relay PW at the same time shitts its armature thereby open- The changeing the battery connections controlled by the relays RE and RW and directly connecting negative battery to the point 19 independently of said polar receiving relays so that the loop circuit will be unaffected during the transmission of the signal, by the receiving relays.

If, while a signal is being received from either the metallic line MLE or the carrier circuit MLlV, it is desired to interrupt for any purpose and transmit in the opposite direction a break signal may be transmitted by opening the loop L thereby causing the polar relays PE and PW to reverse the connections of the circuits RLE and TLE so that a continuous spacing signal will be transmitted to the main line MLE and the carrier circuit MLVV. The sending operator who is at the. moment transmitting over one of these lines will be informed upon the receipt of the continuous spacing signal that another operator desires to send and the sending operator will then cease transmitting. If the loop L should be transmitting and a break signal should be received, the armature of the receiving relay RE or the receiving relay RVV, depending upon w iether the break signal came from the line MLE or the line MLl V, would be shifted to its alternate contact thereby connecting both ends of the loop to the same pole of the battery so that current ceases to flow in the loop. The operator transmitting over the loop circuit'will be apprised of the break signal by noting that the sounder no longer follows the opening and closing of the loop by the sending key.

Fig. 2 illustrates an arrangement similar to Fig. 1 except that the circuit is arranged for full duplex operation. Since in full duplex operation signals may be simultaneously transmitted in both directions through the repeater between the metallic line and the carrier circuit, additional loops are necessary for local operation at the repeater station. Accordingly, a loop LE is provided for transmitting to the metallic line MLE and a loop IIW for transmitting to the carrier circuit MLVV. A loop LE is provided for receiving from the line MLE and a similar loop LVV is arranged to receive from carrier circuit MLVV. The receiving loops LE and Ll are simply arranged so that their circuits are opened and closed by the armatures of the polar relays RE and RVV respectively. The sending loops LE and LlV are balanced by balancing circuits N E and NW respectively and battery is connected to the junction points 19 and 19 of the loops and balancing circuits. The polar relays PE and Pl/V each have a winding in the loop and corresponding balancing circuit and the balancing circuits are so proportioned with respect to the loops LE and LW, or the windings in the loop and balancing circuit are so proportioned with respect to each other that a greater pull in one direction is impressed upon the armature of the relays by the upper windings than is impressed in the opposite direction by the lower windings. The pull due to the upper windings tends to hold the armatures of these relays against their normal contacts but when the loops are interrupted the upper windings are deenergized and the lower windings become effective to shift the arina tures to their alternate contacts.

Signals incoming from the metallic circuit MLE operate upon the amplifying modulator TA in exactly the same manner as in connection with Fig. 1 so that the low frequency signals are transmitted into modulated carrier currents. Likewise modulated carrier currents received from the car rier circuit MLlV operate through the detector D to produce currents of opposite sign in the circuit TLl/V which currents are transmitted over the metallic line MLE. The signals received from the metallic line TLE in addition to actuating the modulator TA causes the polar receiving relay RE to shift its armature and. open the loop LE so that the sounder responds. Likewise the currents of opposite sign impressed by the de tector D upon the circuit TLE in response to modulated carrier current-s actuate the receiving relay Bil to open the loop Lil so that the receiving sounder in said loop responds to the signal incoming from the line lVlLl V.

Signals may be transmitted from the loop LE to the metallic line MLE by opening the loop so that the polar relay PE reverses the connections of the circuit TLE, thereby reversing the polarity of the current transmitted from the detector D to the metallic line MLE. In a like manner, signals may be transmitted from the loop Ll/V to the carrier circuit NPQl/V by interrupting the loop so that the polar relay LW through its armatures reverses the connections between the circuit RLE and the modulating amplifier TA thereby modulating the carrier frequency in the manner already described.

It will be obvious that the general principles herein described may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the following claims.

lVhat is claimed is:

1. In a signaling system, a carrier transmission line, a low frequency telegraph line and a two-way repeater interconnecting said lines, said repeater having channels for transmission in opposite directions, one of said channels including vacuum tube means for modulating carrier currents in accordance with low frequency signaling currents directly impressed upon the grid of said ll i Ill)

vacuum tube means from said low frequency line and the other of said channels including means for translating modulated carrier currents into low frequency signaling currents.

2. In a signaling system, a carrier transmission line, a low frequency telegraph line and a two-way repeater interconnecting said lines, said repeater having channels for transmission in opposite directions, one of said channels includingmeans for translating signaling currents incoming from said telegraph line as currents of opposite sign intecarrier currents of varying amplitude and the other of said channels including means for translating carrier currents of varying amplitude into low frequency sig nal currents of opposite signs.

In a signaling system, a carrier transmission ,line, a low frequency telegraph line and a two-way repeater interconnecting said lines, said repeater having channels for transmission in opposite directions, one of said channels including means for modulating carrier currents in accordance with low frequency signaling currents, the other of said channels including means for translating modulated carrier currents into low frequency signaling currents, and a local subscribers circuit associated with one of said channels for transmitting signals thereto inde endently of said low frequency telegrap line.

4. In a signaling system, a carrier trans mission line, a low frequency telegraph line and a two-way repeater interconnecting said lines, said repeater having channels for transmission in opposite directions, one of said channels including means for modulati -ng carrier currents in accordance with low frequency signaling currents, the other of said channels including means for translating modulated carrier currents into low frequency signaling currents, and a local subscrihers circuit associated with the channel including said modulated means, said suhscribers circuit including means for actuatingjsaid modulatin-gmeans independently of said l w frequency telegraph line.

5. In a signaling system, a carrier transmission line, a low frequency telegraph line and a two-way repeater interconnecting said lines, said repeater having channels for transmission in opposite directions, one of .saidchannels including means for translatsignaling currents incoming from said telegraph line as currents of opposite sign into carrier currents of varying amplitude, the other of said channels including'means for translating carrier currents of varying amplitude into low frequency signal currents cf opposite sign, and a local subscriher s circuit associated with said first mentioned channel, said suloscrihers circuit including .rneans for reversing the connections of the low frequency portion of said channel to produce independent reversals of polarity to actuate said modulator.

6, In a signaling system, a carrier transmission line, alow frequency telegraph line and a two-way repeater interconnecting said lines, said repeater having channels for transmission in opposite directions, one of said channels including means for modulating carrier currents in accordance with low frequency signaling currents, theother of said channels including ineans'for translating modulated carrier currents into low frequency signaling currents, and a, local subscrihers circuit associated with the channel including said translating means, said sat-l scribers circuit including means for ;pr0- ducing low frequency signals in said channel independently of said low frequency tele-' graph line.

7. In a signaling system, a carrier transmission line, a low frequency telegraph line and a two-way repeater interconnecting said lines, said repeater having channels for transmission in opposite directions, one ef said channels incl-udingmeans forgtranslating signaling currents incoming from said telegraph line as cur-rents of opposite, Sign into carrier currents of varyingamplitude, the other of said channels including means for translating carrier currents of varying amplitude into low frequency signal ca;- rents of opposite sign, and a local sub.- scriloers circuit associated withusaidsecond mentioned channel and means in said sub-- scribers circuit for reversing connections of the low frequency portion of saidchannel to transmit'currents of opposite signto said telegraph line.

8, In signaling system, a carrier trailsmission line, a low frequency telegraph line and a two-way repeater "interconnecting said line's,- said repeater having channels for transmission opposite directions, cm of said channels including meansvfor modulating carrier currents, in acccrdance with low frequency signaling currents, thexother of said channels including means for translating modulated carrier currents intolo-w frequency signaling currents, and a local subscribers circuit for receiving signals transmitted through one of said channels from one of said lilies and independently of the other.

9. In a signaling system,- a carrier trails i mission line, a low frequency telegraph line and a twdway repeater interccnriedting said lines, said repeater having :hannsls for transmissien in eofipdsite directidns, 'ne

of said channels including means for mdrtsubscribers circuit for receiving signals transmitted over the channel including said demodulating means independently of said low frequency telegraph line.

10. In a signaling system, a carrier transmission line, a low frequency telegraph line and a two-way repeater interconnecting said lines, said repeater having channels for transmission in opposite directions, one of said channels including means for modulating carrier currents in accordance with low frequency signaling currents, the other of said channels including means for translating modulated carrier currents into low frequency signaling currents, and a local subscribers circuit for receiving signals transmitted over the channel including said translating means independently of said low frequency telegraph line.

11. In a signaling system, a carrier trans mission line, a low frequency telegraph line and a two-way repeater interconnecting said lines, said repeater having channels for transmission in opposite directions, one of said channels including means for translating signaling currents incoming from said telegraph line as currents of opposite sign into carrier currents of varying amplitude, the other of said channels including means for translating carrier currents of varying amplitude into low frequency signal currents of opposite sign, a local subscribers circuit and means associated with said circuit whereby said circuit responds to currents of opposite polarity transmitted over said first mentioned channel.

, 12. In a signaling system, a carrier transmission line, a low frequency telegraph line and a two-way repeater interconnecting said lines, said repeater having channels for transmission in opposite directions, one of said channels including means for translating signaling currents incoming from said telegraph line as currents of opposite sign into carrier currents of varying amplitude, the other of said channels including means for translating carrier currents of varying amplitude into low frequency signal currents of opposite sign, a local subscribers circuit and means associated with said circuit whereby said circuit responds to currents of opposite polarity transmitted over said second mentioned channel.

13. In a signaling system, a carriertransmission line, a low frequency telegraph line and a two-way repeater interconnecting said lines, said repeater having channels for transmission in opposite directions, one of said channels including meansfor modulating carrier currents in accordance With low frequency signaling currents, the other of said channels including means for translating modulated carrier currents into low frequency signaling currents, and a local subscmbers 6l10l }i '&SSOOia,t9d. with said tasters channels, said subscribers circuit including means for transmitting signals to both channels independently of said low frequency telegraph line. w

14. In a signaling system, a carrier transmission line, a low frequency telegraph line and a two-way repeater interconnecting said lines, said repeater having channels for transmission in opposite directions, one of said channels including means for translating signaling currents incoming from said telegraph line as currents of opposite sign into carrier currents of varying ampli tude, the other of said channels including means for translating carrier currents of varying amplitude into low frequency signal currents of opposite sign, and a local subscribers circuit, said subscribers circuit including means for independently transmitting currents of opposite signs over said channels by reversing the connections of said channels. 7

15, In a signaling system, a carrier transmission line, a low frequency telegraph line and a two-way repeater interconnecting said lines, said repeater having channels for transmission in opposite directions, one of said channels including means for modulating carrier currents in accordance with low frequency signaling currents, the other of said channels including means for translating modulated carrier currents into low frequency signaling currents, and a local subscribers circuit independent of said low frequency telegraph line, said circuit including means for transmitting sigs to either of said channels and also including means responsive to signals transmitted over either channel.

16. In a signaling system, a carrier transmission line, a low frequency telegraph line and a two-way repeater interconnecting said lines, said repeater having channels for transmission in opposite directions, one of said channels including means for translating signaling currents incoming from said telegraph line as currents of opposite sign into carrier currents of varying amplitude, the other of said channels including means for translating carrier currents of varying amplitude into low frequency signal currents of opposite sign, a local subscribers circuit, means associated with said circuit for reversing the connections of the low frequency portion of either of said channels and means associated With said subscribers circuit responsive to signals transmitted over either of said channels.

17. In a signaling system, a detector circuit for translating carrier currents into direct currents of opposite sign, said detector circuit comprising a VVheatstone bridge having a detector element Whose impedance varies with the amplitude of carr r n s formi g one arm of said bridge, and a circuit to be supplied with currents of opposite polarity connected to opposite points of the bridge.

18. In a signaling system, a detector circuit for translating carrier currents into direct currents of opposite sign, said detector circuit comprising a WVheatstone bridge arrangement, a vacuum tube element forming one arm of the bridge, said vacuum tube element being so constructed that in response to carrier currents of certain amplitudes its impedanceis such as to unbalance the bridge in one direction and in response to carrier currents of other amplitudes its impedance is such as to unbalance the bridge in the other direction, and a circuit to be supplied with currents of opposite polarity connected to opposite points of said bridge.

19. In a signaling system, a modulating arrangement for translating direct currents of opposite sign into modulated carrier currents, said modulating arrangement comprising a modulating element and polarizing source for said element, said polarizing source having such a potential that When direct currents of one polarity are superposed upon said source the impedance of said modulating element becomes a minimum for carrier currents and When a direct current of the opposite polarity is superposed on said source the impedance of said element becomes a maximum for carriercurrents.

20. In a signaling system, a modulating arrangement for translating direct currents of opposite signs into carrier currents, said modulating arrangement comp-rising a modulating vacuum tube amplifier, means to supply carrier currents thereto and a polarizing source for said amplifier, the potential of said source being such that When direct currents of one sign are superposed upon said source the amplification of said amplifier for carrier currents Will be a maximum, but When direct currents of the opposite sign are superposed upon said source the amplification of said amplifier for carrier currents Will be a minimum.

21. In a signaling system, means to transm it carrier currents of varying amplitudes, and a translating device to translate the carrier currents into direct current impulses oi opposite polarity.

In a signaling system, means to transmit direct current signaling impulses of opposite polarity, and means to translate the direct current signaling impulses into a carrier frequency varying in amplitude.

In testimony whereof, Ihave signed my name to this specification this 19th day of October, 1920.

LLOYD ESPENSGHIED. 

